The current proposal represents closely integrated basic science, preclinical and clinical investigations of the role of cytokine-inducible nitric oxide synthesis as an effector mechanism during cancer immunotherapy with interleukin-2 (IL-2). Since glutathione appears to be a cofactor for the nitric oxide synthase, the goal of the proposed studies is to develop a better understanding of the interrelationship of glutathione biosynthesis with IL-2 induced macrophage and lymphocyte antitumor mechanisms. In Program 1 we will develop cellular and basic science models to evaluate the role of sulfhydryl compounds, such as glutathione and cysteine in regulating the function of the L-arginine dependent pathway of nitric oxide synthesis. These studies will also focus on developing a better understanding of the effector mechanisms of this pathway on a molecular level. Using the cysteine analogue N-acetyl cysteine (NAC) we hope to increase glutathione synthesis in cells and in vivo, and to increase the activity of the cytokine inducible nitric oxide synthase. Since NAC unexpectedly augmented lymphocyte activation by IL-2, as well as improving therapeutic responses to IL-2 in a subcutaneous murine tumor model, we will also evaluate the effects of this agent on cytotoxic lymphocyte function. In Program 2 we will perform the initial toxicity testing of NAC in high-dose IL-2 treated patients. This agent has already been safely used in patients to counteract drug and heavy metal intoxications. The proposed studies will evaluate the maximum tolerated dose of NAC, as well as the dose limiting toxicity. During this Phase IA trial, we will also evaluate the pharmacokinetics of NAC during IL-2 administration. The effect of NAC on the cytokines that induce NO. synthase, the metabolic intermediates of the L-arginine dependent pathway, as well as on the effector mechanisms of this pathway will be evaluated during the course of the clinical study. This combined program should contribute to a better understanding of the role of nitric oxide as an effector mechanism in IL-2 therapy and its role in IL-2 related toxicity. The long term goal of these studies is increase the effectiveness of IL-2 therapy by modulating the activity L-arginine dependent pathway via cysteine analogues.